Not Applicable.
The present invention relates to an alignment guide for ensuring proper alignment or orientation of a prosthetic stem in bone.
Stems are used in prosthetic joint implants to anchor the implant in a bone cavity. The bone for receiving the stem is typically prepared by drilling a hole in the bone and creating an opening sized and contoured to receive the stem of the implant. The stem is inserted into a prepared cavity of a bone and a joint bearing surface attached or coupled to the stem, extends out to the cavity. Many stems are fluted, i.e., they have distally extending longitudinal grooves in the stems that provide greater stability and anchoring of the stem once it is inserted into the prepared cavity.
Typically, once a fluted stem is inserted into a prepared cavity, it is extremely difficult to rotate the stem to properly reorient it. In order to do so the stem must be removed and reinserted which can damage bone and increase operative time. Typically, the stem is aligned by marking the bone and the stem and using the marks to align the stem with respect to the bone. The drawback to this method is the potential imprecision in the alignment. Because the landmark on the stem and bone are not in close proximity to each other, parallax and other problems associated with alignment by eye may result. Also, the stem may move from its aligned position as it is inserted.
Accordingly, it is an object of the present invention to provide a means for aligning a fluted stem of an orthopedic implant prior to and as it is being inserted into a prepared bone cavity.
The present invention provides a method and device for inserting a keyed or fluted prosthetic component in an aligned position into a prepared bone cavity. The bone is prepared by removing bone material from the bone canal and by machining an opening of a predetermined shape in the bone cavity. An alignment guide having an outer shape conforming with that of the machined opening is inserted into the bone cavity. The alignment guide also has an inner shape or key element corresponding to the outer shape of the fluted stem of the implant that engages the stem, preferably in a manner which provides contact with a small area of the stem. In a preferred embodiment the inner shape of the alignment guide includes notches or grooves for receiving the flutes of the stem. Another aspect of a preferred embodiment may provide protrusions in the alignment guide that make contact with certain keyed elements of the prosthesis to be inserted.
In a preferred embodiment, the alignment guide is formed generally in a broken circle or circumference to allow flexibility in removing the alignment guide. The alignment guide further comprises a means for lifting the alignment guide from the bone cavity once the stem is inserted through the alignment guide. This means may, for example, be a tab or protrusion or an opening for inserting a tool to pry out the guide. In a further embodiment, the alignment guide includes a guide body that is disposed at the distal end of a handle.
In a preferred embodiment, once the bone cavity is prepared and the alignment guide is inserted, a fluted stem of a prosthetic implant is positioned or oriented with respect to the stem axis and is then inserted into the alignment guide with the flutes extending into the notches of the alignment guide. Once the stem is inserted in the guide, the position or orientation is held true until the stem is seated into the bone cavity. As the stem is inserted, the flutes form a path within the bone cavity that the stem will generally follow during the insertion of the final segment of the stem. Once this has occurred the alignment guide may be removed by pulling the tab. The insertion is completed by extending the implant all the way into the opening until the proximal geometry of the stem is placed within the machined opening in the bone. This stem proximal geometry is also of a shape that corresponds to the machined opening so that the implant fits within the bone cavity.